Replace hidden flag with post state.

Store post state as text so Go owns the allowed values and future states such as locked remain representable without a database enum migration.

internal/store/post_test.go

@@ -50,6 +50,9 @@ func TestMemoryPostLifecycle(t *testing.T) {
 	if err := mem.CreatePost(ctx, root); err != nil {
 		t.Fatal(err)
 	}
+	if root.PostState != PostStateVisible {
+		t.Fatalf("default post state = %q, want visible", root.PostState)
+	}
 
 	rootID := root.ID
 	later := &Post{
@@ -175,6 +178,24 @@ func TestMemoryPostValidation(t *testing.T) {
 				Body:     "Body",
 			},
 		},
+		{
+			name: "invalid post state",
+			post: &Post{
+				AuthorID:  homeowner.ID,
+				Title:     "Invalid state",
+				Body:      "Body",
+				PostState: PostState("archived"),
+			},
+		},
+		{
+			name: "reply with non-visible state",
+			post: &Post{
+				ParentID:  ptr("missing"),
+				AuthorID:  homeowner.ID,
+				Body:      "Body",
+				PostState: PostStateLocked,
+			},
+		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
@@ -185,12 +206,12 @@ func TestMemoryPostValidation(t *testing.T) {
 	}
 
 	hidden := &Post{
-		ID:       "hidden",
-		AuthorID: homeowner.ID,
-		Title:    "Hidden",
-		Body:     "Body",
-		PostDate: "2026-08-26",
-		Hidden:   true,
+		ID:        "hidden",
+		AuthorID:  homeowner.ID,
+		Title:     "Hidden",
+		Body:      "Body",
+		PostDate:  "2026-08-26",
+		PostState: PostStateHidden,
 	}
 	if err := mem.CreatePost(ctx, hidden); err != nil {
 		t.Fatal(err)
@@ -199,6 +220,28 @@ func TestMemoryPostValidation(t *testing.T) {
 		t.Fatalf("hidden root vote error = %v", err)
 	}
 
+	locked := &Post{
+		ID:        "locked",
+		AuthorID:  homeowner.ID,
+		Title:     "Locked",
+		Body:      "Body",
+		PostDate:  "2026-08-26",
+		PostState: PostStateLocked,
+	}
+	if err := mem.CreatePost(ctx, locked); err != nil {
+		t.Fatal(err)
+	}
+	if err := mem.VotePost(ctx, homeowner.ID, locked.ID, 1); err != nil {
+		t.Fatalf("locked root should remain votable: %v", err)
+	}
+	roots, err := mem.ListRootPosts(ctx, locked.PostDate, homeowner.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(roots) != 1 || roots[0].ID != locked.ID || roots[0].PostState != PostStateLocked {
+		t.Fatalf("locked root should remain visible: %+v", roots)
+	}
+
 	if _, err := mem.GetPostThread(ctx, "missing"); !errors.Is(err, sql.ErrNoRows) {
 		t.Fatalf("missing thread error = %v", err)
 	}